If you are using it as a substitute for paper in hard to reach areas then the red pad is what you want to use. Follow up with the grey pad and Scuff-Stuff if you have some, over the entire vehicle. Because it is relatively fine (grit/scratch) the only way the gray pad is effective is using it with Scuff-Stuff (Presta) or something similar. Plus the scuff-stuff cleans the surface really well which is the main reason for using it.